Eventing Source to Sink

Before beginning to run the exercises, navigate to the tutorial chapter’s eventing folder:

cd $TUTORIAL_HOME/eventing

Event Source

Knative Eventing Sources are software components that emit events. The job of a Source is to connect to, drain, capture and potentially buffer events; often from an external system and then relay those events to the Sink.

Knative Eventing Sources installs the following four sources out-of-the-box:

kubectl api-resources --api-group='sources.knative.dev'

NAME               SHORTNAMES   APIVERSION               NAMESPACED   KIND
apiserversources                sources.knative.dev/v1   true         ApiServerSource
containersources                sources.knative.dev/v1   true         ContainerSource
pingsources                     sources.knative.dev/v1   true         PingSource
sinkbindings                    sources.knative.dev/v1   true         SinkBinding

Let’s see how a simple source, the PingSource looks like :

eventinghello-source.yaml

apiVersion: sources.knative.dev/v1
kind: PingSource (1)
metadata:
  name: eventinghello-ping-source
spec: (2)
  schedule: "*/2 * * * *"
  data: '{"key": "every 2 mins"}'
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: eventinghello

1	The type of event source, the eventing system deploys a bunch of sources out of the box and it also provides way to deploy custom resources
2	spec will be unique per source, per kind

Referencing the Event Sink

Knative Eventing Sink is how you specify the event receiver — that is the consumer of the event--. Sinks can be invoked directly in a point-to-point fashion by referencing them via the Event Source’s sink as shown below:

eventinghello-source.yaml

apiVersion: sources.knative.dev/v1
kind: PingSource
metadata:
  name: eventinghello-ping-source
spec:
  schedule: "*/2 * * * *"
  data: '{"message": "Thanks for doing Knative Tutorial"}'
  sink:  (1)
    ref:
      apiVersion: serving.knative.dev/v1 (2)
      kind: Service
      name: eventinghello (3)

1	sink can target any Kubernetes Service or
2	a Knative Service
3	Deployed as "eventinghello"

Event Source can define the attributes that it wishes to receive via the spec. In the above example it defines schedule(the cron expression) and jsonData that will be sent as part of the event.

When you watch logs, you will notice this data being delivered to the service.

Create Sink Service

Run the following command to create the Knative service that will be used as the subscriber for the cron events:

eventing-hello-sink.yaml

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: eventinghello
spec:
  template:
    metadata:
      name: eventinghello-v1
      annotations:
        autoscaling.knative.dev/target: "1"
    spec:
      containers:
      - image: quay.io/rhdevelopers/eventinghello:0.0.2

Deploy Sink Service

Run the following commands to create the service:

kn
kubectl

kn service create eventinghello \
  --concurrency-target=1 \
  --image=quay.io/rhdevelopers/eventinghello:0.0.2

kubectl apply -f ${TUTORIAL_HOME}/eventing/eventing-hello-sink.yaml

Create Event Source

Run the following commands to create the event source resources:

kn
kubectl

kn source ping create eventinghello-ping-source \
  --schedule "*/2 * * * *" \
  --data '{"message": "Thanks for doing Knative Tutorial"}' \
  --sink ksvc:eventinghello

kubectl apply -f ${TUTORIAL_HOME}/eventing/eventinghello-source.yaml

Verification

kn
kubectl

kn source ping list

Running the above command should return the following result:

NAME                        SCHEDULE      SINK                 AGE   CONDITIONS   READY   REASON
eventinghello-ping-source   */2 * * * *   ksvc:eventinghello   9s    3 OK / 3     True

kubectl get pingsources.sources.knative.dev \
  eventinghello-ping-source

Running the above command should return the following result:

NAME                        SINK                                                     AGE   READY   REASON
eventinghello-ping-source   http://eventinghello.knativetutorial.svc.cluster.local   47s   True

If you haven’t already, you can watch logs to see the ping job source sending an event every 2 minutes:

stern eventinghello -c user-container -n knativetutorial

...
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,427 INFO  [eventing-hello] (executor-thread-1) ce-id=4b59c201-56a3-4189-b042-4246d3f33504
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,501 INFO  [eventing-hello] (executor-thread-1) ce-source=/apis/v1/namespaces/user2-knativetutorial/pingsources/eventinghello-ping-source
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,501 INFO  [eventing-hello] (executor-thread-1) ce-specversion=1.0
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,501 INFO  [eventing-hello] (executor-thread-1) ce-time=2021-01-28T08:14:00.000224506Z
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,502 INFO  [eventing-hello] (executor-thread-1) ce-type=dev.knative.sources.ping
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,502 INFO  [eventing-hello] (executor-thread-1) content-type=application/json
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,502 INFO  [eventing-hello] (executor-thread-1) content-length=47
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container 2021-01-28 08:14:05,502 INFO  [eventing-hello] (executor-thread-1) POST:{"message":"Thanks for doing Knative Tutorial"}
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container I> No access restrictor found, access to any MBean is allowed
eventinghello-00001-deployment-c8f4f6758-qrjm6 user-container Jolokia: Agent started with URL https://10.129.4.97:8778/jolokia/

Cleanup

kn
kubectl

kn source ping delete eventinghello-ping-source
kn service delete eventinghello

kubectl delete -f ${TUTORIAL_HOME}/eventing/eventinghello-source.yaml
kubectl delete -f ${TUTORIAL_HOME}/eventing/eventing-hello-sink.yaml